In communication networks, a user may be identified by a subscription identity. The subscription identity may for example be used for authenticating the user in the communication network. One example of a subscription identity is the MSISDN (Mobile Subscriber Integrated Services Digital Network Number) as used in 3GPP (Third Generation Partnership Project) mobile networks and other types of mobile networks. The subscription identity is assigned to the user on a long-term basis, e.g., for the duration of a contract agreement between the user and an operator of the communication network.
Further, a user may also be identified on the basis of a transport address, e.g., an IP (Internet Protocol) address, as used for transmitting data to or from the user. Typically, if the user uses a certain user equipment (UE) for connecting to the communication network, such a transport address may be assigned to the UE by the communication network. As compared to the subscription identity, the assignment of the transport address is on a short-term basis, e.g., for the duration of data communication between the user and the communication network. Also, the transport access may change when the user disconnects from the communication network and later connects or attaches again.
In some scenarios, a node involved in data communication with the user may be aware of the transport address, but not of the subscription identity of the user. One example of such scenarios can be found in the PCC (Policy and Charging Control) architecture as defined in 3GPP Technical Specification (TS) 23.203. In this case, an Application Function (AF) may be a third-party node offering a certain service to the users of the mobile network. For transmitting service-related data to and from the UE of the user, the AF is aware of the IP address assigned by the mobile network to the user. However, for privacy reasons, the third-party AF may not be aware of the subscription identity of the user. For enabling the control of Quality of Service (QoS), the AF may communicate with a Policy and Charging Rules Function (PCRF) of the mobile network. In communication with the PCRF, the AF may use the IP address for identifying the user. This IP address is assigned to the user on a temporary basis. For example, if the UE of the user detaches from the mobile network at some time, it will typically loose the IP address assigned by the mobile network. The IP address may then be assigned to some other user. When the UE reattaches to the mobile network, it may be assigned a new IP address which may be different from the previous one.
In view of its above-described temporary character, the IP address assigned to the user by the mobile network has some limitations when used by the AF for identifying the associated user. For example, monitoring usage of the service by the user on a long-term basis would be problematic since the user's UE may frequently detach from the mobile network and reattach to the mobile network and therefore use different IP addresses in communication with the AF.
Accordingly, there is a need for techniques which allow for more accurate identification of a user of a communication network while at the same time taken into account privacy aspects.